Biological Explanations of Aggression

Question 1

What animal example suggests a biological explanation of aggression?

Answer 1

1. Species of various animals have been selectively bred to produce highly aggressive individuals, e.g. Doberman dogs were originally bred by humans to behave aggressively towards intruders so they can be used as guard dogs,
2. This ability to select the most aggressive dogs and breed them together to give new generations with the same aggressive tendencies suggests that there are specific genes that determine levels of aggression.

Question 2

Christiansen (1977), method?

Answer 2

1. An analysis of criminality in 3586 pairs of twins born between 1881 and 1910 in a region of Denmark was conducted, in order to find concordance rates,
2. Of this sample, 926 individuals were registered by the police for criminal activity. Identical and non-identical twins were compared for the rate at which both twins of the pair were registered.

Question 3

Christiansen (1977), results?

Answer 3

1. Male MZ twins showed 35% concordance rates for criminality, compared to 12% concordance shown between DZ twins,
2. Female MZ twins showed 21% concordance compared to 8% for DZ twins.

Question 4

Christiansen (1977), conclusion?

Answer 4

1. Twins of criminals are more likely to also be criminals if they share all of their twin’s genes, rahter than only some of their genes,
2. So there is a genetic component to aggressive behaviour.

Question 5

Christiansen (1977), evaluation?

Answer 5

1. Genetics can’t be the only factor, as the concordance rate for MZ twins wasn’t 100%,
2. By studying all the twins born in a specified time-frame, this study gives a representative rate of concordance,
3. However, as with all twin studies, environment might account for the different concordance rates - because they look the same, MZ twins may be treated more alike, and have more shared experiences.

Question 6

What is MAOA?

Answer 6

1. Monoamine oxidase A,
2. An enzyme involved in processing neurotransmitters, including serotonin, in the brain.

Question 7

How is MAOA linked to aggression?

Answer 7

1. Serotonin is thought to be involved in aggression,
2. The MAOA gene controls production of MAOA,
3. Some versions of the gene, which result in lower levels of MAOA (therefore lower levels of serotonin processed in the brain) have been linked to aggressive behaviour.

Question 8

Brunner et al. (1993), method and findings in relation to MAOA and aggression?

Answer 8

1. Studied an extended family in the Netherlands, where several male family members showed patterns of behaviour involving impulsive aggression, including violent crime,
2. They identified a fault in the MAOA gene of the individuals who showed impulsive aggression, which wasn’t present in other male family members,
3. The individuals with this fault were deficient in MAOA.

Question 9

What animal study found a relationship between MAOA gene variations and aggression?

Answer 9

1. Cases et al. (1995) found that adult male mice who were missing the MAOA-producing gene had specific behaviour patterns, which included heightened aggression,
2. This is known as a knockout study - animals are bred so that they are missing a specific gene, and are then studied to observe the effect of the gene.

Question 10

Strengths of the genetic explanation?

Answer 10

1. Twin studies, adoption studies, and knockout studies suggest there is a genetic element to aggression,
2. Caspi et al. (2002) found that men with a ‘low MAOA activity’ gene were not significantly more likely to engage in anti-social behaviour, including violence. However, there was a significant effect in men who had been maltreated as children. This suggests that genetics interact with environmental factors to influence aggression levels.

Question 11

Weaknesses of the genetic explanation?

Answer 11

1. The genetic explanation ignores social and environmental factors, which may play a part too,
2. Walters’ (1992) meta-analysis found only a weak correlation between genetic factors and crime. This effect was weaker for more recent and better designed studies.

Question 12

What area of the brain has been linked to aggression?

Answer 12

1. Different areas of the brain, including the temporal lobe and the limbic system, have been linked to different forms of aggressive behaviour,
2. One part of the limbic system, the amygdala, has been found to have a particularly strong connection to aggression.

Question 13

What have animal studies shown of neurological factors involvement in aggression?

Answer 13

Animal studies have shown that electrical stimulation of different parts of the amygdala can either cause or reduce aggression. Lesions to the amygdala have been found to cause cats to attack, but caused dogs to become more submissive and less aggressive - they needed stimulation to provoke a response.

Question 14

What example shows neurological factors involved in human aggression?

Answer 14

1. Charles Witman, a sniper who killed 14 innocent people and wounded 31 others,
2. He left a note that pleaded for his brain to be examined after death for possible dysfunction,
3. An autopsy showed that he had a temporal lobe tumour, pressing on his amygdala.

Question 15

What is an amygdalatomy?

Answer 15

1. A procedure which involves disconnecting the amygdala from the rest of the brain,
2. Studies have shown that, following the procedure, many patients experience a loss of emotion and become a lot less aggressive.

Question 16

Mpakopoulou et al. (2008) findings?

Answer 16

1. Conducted a review looking at studies investigating aggression in patients before and after an amygdalotomy,
2. Of the 13 patients they looked at, they found that, overall, aggressive behaviours in those who’d had an amygdalotomy had decreased between 33 and 100% with no impact on the patients’ learning or intelligence.

Question 17

How is level of serotonin in the brain measured?

Answer 17

Measured by turnover - this how much serotonin is produced and then broken down.

Question 18

Higley et al. (1996), method and findings on serotonin and aggression?

Answer 18

1. Studied a group of 49 rhesus monkeys over 4 years,
2. They determined each individual’s serotonin turnover,
3. Monkeys with lower serotonin turnover were observed to be more aggressive. After 4 years, 11 monkeys had died or were missing,
4. All of the monkeys in the highest serotonin turnover group survived, and the 4 monkeys who had died as a result of aggressive encounters were all in the lowest serotonin group.

Question 19

Valzelli and Bernasconi (1979), method and findings?

Answer 19

1. Bred mice with low serotonin turnover,
2. They found that, when isolated, these mice were more aggressive than mice with normal serotonin turnover.

Question 20

How can diet manipulation studies affect aggression?

Answer 20

1. Use contolled diets to attempt to manipulate brain serotonin levels in healthy participants,
2. Serotonin is made from an amino acid called tryptophan. A diet low in tryptophan, but high in other amino acids, is thought to reduce brain serotonin levels.

Question 21

Moeller et al. (1996), findings?

Answer 21

1. Found that healthy male subjects showed increased aggression 5/6 hours after they were given a typtophan-free mixture of amino acids,
2. The researchers proposed that this aggression was likely to have been caused by decreased serotonin levels in the participants’ brains.

Question 22

Weaknesses of studies linking sertonin with aggression?

Answer 22

1. Animal studies show a strong link between low serotonin turnover and aggression, but this doesn’t mean the link is causal. Also findings from animal studies cannot be generalised to humans,
2. Studies using diet are better controlled, and usually involve healthy participants. However, they don’t directly link serotonin to aggression - it is just thought that this is why a controlled diet can affect aggression,
3. Laboratory studies have low ecological validty. Natural experiments have higher ecological validity, and these studies tend to support a more complicated relationship between serotonin and aggression.

Question 23

Virkkunen et al. (1987), findings?

Answer 23

1. Studied serotonin turnover in 20 arsonists, 20 violent offenders, and 10 healthy volunteers,
2. Serotonin turnover was significantly lower in the arsonists than in the other groups. However, serotonin turnover didn’t correlate with the severity of the arsonist’s offences,
3. Virkkunen et al. proposed that this showed a link between serotonin and impulsive behaviour, rather than aggressive behaviour.

Question 24

Weakness of Virkkunen et al.

Answer 24

Results from convicted criminals may not be generalisable to the population as a whole.

Question 25

Testosterone's involvement in aggression?

Answer 25

1. Testosterone is an androgen (male sex hormone) - it is responsible for the development of male characteristics, and may also affect the brain, 2. Men produce much more testosterone than women, and men are statistically more likely to engage in violence than women. For example, a very high proportion of people arrested for violence against another person in the UK are men, 3. It has been suggested that his indicates that testosterone is related to aggression.

Question 26

Dabbs et al. (1987), method and findings?

Answer 26

1. Measured testosterone levels in the saliva of 89 male prison inmates, 2. Those with higher testosterone concentration were more likely to have been convicted of violent crimes, 3. Almost all of those with the highest levels had been convicted of violent crimes, and almost all of those with the lowest levels had been convicted of non-violent crimes.

Question 27

Issue with Dabbs et al.?

Answer 27

1. There is a problem with establishing cause and effect, 2. This data is only correlational, 3. Another factor could be causing aggression, or it could be that being aggressive raises levels of testosterone.

Question 28

What did Van Goozen et al. (1994) do differently from Dabbs et al. (1987)?

Answer 28

1. Studied the effects of testerone directly, 2. This avoided having to depend on correlational data, which made it easier to establish cause and effect.

Question 29

Van Goozen et al. (1994), method?

Answer 29

1. In a repeated measures design, 50 transgender people transitioning to the gender that they identified as, using hormone therapy, completed questionnaires to assess proneness to aggression, 2. They completed the questionnaires before and after receiving hormones, 3. Those transitioning from female to male were given testosterone and those transitioning from male to female were given anti-androgens. Treatment lasted 3-months.

Question 30

Van Goozen et al. (1994), results?

Answer 30

People transitioning from female to male reported an increase in aggression proneness, whereas those transitioning from male to female reported a decrease.

Question 31

Van Goozen et al. (1994), conclusion?

Answer 31

1. Levels of testosterone determine the likelihood of displaying aggressive behaviours.

Question 32

Van Goozen et al. (1994), evaluation?

Answer 32

1. By controlling levels of testosterone experimentally, the direction of cause and effect between testosterone and aggression can be established, 2. However, self-report measures of aggression were used, which are subjective and so may not be valid, 3. The participants may have been conforming to stereotypes of their new gender roles by expressing an increase or decrease in aggression.